Among the X ray CT systems of the tomographic systems, the multi-slice X ray CT system, which can obtain plural tomographic images in the axial direction of the body of the subject, etc., is used in increasingly many cases in recent years. In order for making able to obtain tomographic images for each of the plural tomographic positions (slice positions) set in the axial direction of the body of the subject, etc. simultaneously the multi-slice tomographic system is equipped with a two-dimensional detector as a means for detecting X ray. The two dimensional detector consists of plural arrays of X ray detection element arrays in which X ray detection elements are arranged linearly, and can performs multi-slice X ray CT imaging by obtaining projection data with each of the plural X ray detecting element array as a unit or with a certain number of X ray detection element arrays as a unit.
Such tomographic systems are used in the examination of the subject or the treatment of the patient with the method known as CT fluoroscopy. The CT fluoroscopy is used in biopsy, where the tissue is taken for examination with a puncture needle from the tumor site in the subject, etc., by inserting a treatment device such as puncture needle into the intended treatment area (the primary tumor site in case of tumor biopsy of the subject, etc.,) and performing necessary procedures (such as obtaining the tissue for examination).
The technology associated with the conventional CT fluoroscopy is to assist the determination of the position from which treatment device is inserted by displaying the plural time-series tomographic images successively (See Patent Document 1).    Patent document 1: Japanese Patent Application Laid-Open No. 2000-287962
However, according to the afore-mentioned patent document 1, the position from which the treatment device is inserted should be determined before insertion of the device into the subject, etc. Therefore, the information required for determining the insert position may not be obtained only from the successive and time-series displayed images in some cases, in which the tomographic images must be taken in the trial and error process. Tt means that the needs for assisting the insertion of the treatment device, namely the needs for reducing the trouble of such trial and error process, cannot be served. Moreover, such needs include not only greater convenience for the operator who performs the treatment, such as improved throughput of diagnosis and examination, but also the advantages for the subjects, etc., who receive examination or treatment, such as reduced X ray exposure dose and shortened hours of treatment.